THX dipole surround speakers degraded direct sound while failing to create genuine diffusion.

Evidence

THX also introduced bidirectional out-of-phase loudspeakers (incorrectly called dipoles) to attenuate the direct sound and add additional reflections to the surround sound field, claiming that the added “diffusion” would be advantageous. Diffusion is a property of a sound field, not a perception, so there was some marketing bias here. Small listening rooms are too acoustically “dead” to support a diffuse sound field. The real problem with this innovation was that the chosen design of these loudspeakers seriously degraded the sound quality of the important direct sound, while the added reflections came from directions ineffective at producing the interaural differences that yield the desired spatial perceptions. — Toole, Floyd E, Sound reproduction- the acoustics and…, 762

Categorization

• DEFINE: Clarifies that diffusion is a property of a sound field, not a perception, and distinguishes bipole (in-phase) from incorrectly-named dipole (out-of-phase) configurations.
• XREF: Connects to the reader’s interest in psychoacoustic models of spatial perception - the claim that reflected sound must arrive from directions that produce interaural differences connects to binaural hearing research.